On the calculation of diffusion coefficients in confined fluids and interfaces with an application to the liquid-vapor interface of water

A general method to calculate the self-diffusion coefficient tensor from molecular dynamics (MD) in a finite region is proposed. The results revealed that far from the interface the diffusion tensor is found of distance as expected, and the diffusion coefficient has the value D approximately is 0.22 A degree 2/ps, in agreement with what is found in the bulk liquid.